Maintaining synchronous rotation of dynamo-electric machines.



No. 732,114. PATENTED JUNE 30, 1903.: E. W.'RIGE', JR. & J. BERG. MAINTAINING SYNOHRONOUS ROTATION 0P DYNAMO ELECTRIC MACHINES.

APPLICATION IILI ED AUG. 28, 1899.

2 SHEETS-SHEET 1.

N0 MODEL.

invehtors. Eldwin'W. Rice, Jr.

:Witnesses.

No. 732,114. PATENTBD JUNE 30,1903. E. W. RICE, In. & E. J. BERG. MAINTAINING SYNGHRONOUS ROTATION 0F D'YNAMO ELECTRIC MACHINES.

APPLIUATIOH FILED AUG. 28, 1899.

K0 MODEL. 2 SHEETS-SHEET 2.

Fig.5.

Fig.4. 9

Inven'bo'fs'. Witnesses Edwin WJqice, Jn,

Ern so J. Berg,

m5 NIJRRS N. o c.

UNITED STATES Patented June 30, 1903.

PATENT OFFICE.

EDWIN WV. RICE, JR, AND ERNST J. BERG, OF SCHENECTADY, NEW YORK, ASSIGNORS TO THE GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

MAINTAINING SYNCHRONOUS ROTATION OF DYNAMO-ELECTRIC MACHINES.

SPECIFICATION forming part of Letters Patent No. 732,114, dated June 30, 1903.

Application filed August 28, 1899. Serial No. 728,651. (No model.)

To all whom, it may concern:

Be it known that we, EDWIN W. RIoE,Jr. and ERNST J. BERG, citizens of the United States, and residents of Schenectady, county of Schenectady, State of New York, have in- Vented certain new and useful Improvements in Maintaining Synchronous Rotationof Dynamo-Electric Machines, of which the following is a specification.

IO The invention herein described relates to a method of securing uniform rotation of one or more alternating-current dynamo-electric machines normally operating in synchronism with another machine or machines.

:5 The phenomenon which it is the object of this invention to prevent consists of a poriodic variation in speed of dynamo-electric machines, which has come to be knownin the art as hunting and may be characterized as the result of a superposition of an oscillation upon a speed of uniform angular ve locity. Our invention is particularly useful in connection with rotary converters, since these 2 5 machines are particularly subject to this trouble; but it is in no sense to be considered as limited thereto, but will be found useful in connection with synchronous motors and other machines as. well. The concrete embodiment of our invention,

while simplein structure, will best be understood in its mode of operation by first consid- I ering in a general way the nature of the phenomena with which it deals. The hunting of converters occurs in either of two forms or as a complication of both one a pulsation in the speed of the converter corresponding with a pulsation of the prime mover due to irregularity in driving power, the other a pulsation in the speed of the converter with a period of its own, the latter depending upon various circumstances, the more important of which are the moment of inertia of the armature and the strength of the field.

If the hunting of the converteris due principally to the varying frequency of the current supplied from the source of power, it can never be entirely cured by the application of any device to the converter itself, since the difficulty is inherent in the operation of l the source of supply. The difficulty can, however, be made insignificant and its accumulative effect avoided by the use of our invention. 5

The hunting inherent in the operation of the converter itself is due to the fact that the armature of the machine does not always keep rigidly in step or in phase with the impressed alternating wave, but may slip backward or forward from the neutral position or position corresponding to uniform rotation. The converter-armature always tends to assume this neutral position, but may vibrate about the same back and forth much in the same Way as a pendulum vibrates back and forth across the point corresponding to its position ofrest. If while the converter-armatu re is in a condition of uniform rotation there occurs some change in the conditions of opera- 7o tionwhicheifectthepullbetweenthe armature and the fieldsuch, for instance, as a sudden change or pulsation in frequency of the current supplied or a change in voltage or a change in l0adthen the uniform rotation of the converter-armature is disturbed and the armature is either dragged back or pulled forward from its neutral position. Instead, however, of instantly assuming a new neutral position the armature vibrates like a pendulum back and forth with a rate dependent upon various factors and often with such amplitude as to cause violent fluctuations or surges in the current supplied to the machine and in the voltage at its terminals, and if the condi- 8 tions are such as to cause an accumulative effect the machine may actually be thrown out of synchronism.

. The means to be employed in preventing the occurrence of the phenomena described 0 must obviously be such as will dampen out the initial oscillations in speed and prevent their accumulative effect. Those'factors in the operation of the converter which tend to increase hunting 'or to lessen it will be'de- 5 scribed only in so far as they may be of use toward an understanding of our invention.

In the converter-armature the reactions of the direct current and the energy component of the alternating current are equal and op roo posite, and thus neutralize each other, while the armature reaction of the wattless component of the alternating current is either in phase or in opposition to the field, thus strengthening or weakening the same, as the case may be. If, however, from any cause, such as those mentioned, the con verter-armature shifts from its neutral position, the alternating armaturere action shifts with it, while the direct-current reaction remains stationary in the position of the commutatorbruslies, thus disturbing the balance between the two armature reactions and producing a resultant magnetomotive force or reaction acting in the space between the field-poles. This magnetomotive force gives rise to a fiux of greater or less magnitude, which fiux for convenience we may term the interpolar flux. This flux may be considered as made up of two components, one acting at right angles to the field-flux, the other either in phase or in opposition to it. The first acts upon each pole as a cross-magnetizing fiux, strengthening one pole-corner and weakening the other, or the reverse, but has no other effect upon the field,while the other increases or decreases the strength of the field. We have found that creating opposition to either of these two results or effects is equivalent to opposing the cause which produced them.

it has heretofore been proposed to encircle the field-poles of the rotary converter with short-circuited windings in order to oppose that component of armature reaction which tends to vary the strength of the field. \Ve have discovered,- however, that this is a distinct disadvantage, and this conclusion has been verified in practice. The field structure necessarily consists of a large mass of magnetic material, which by reason of hysteresis, eddy-currents, and other causes which produce a lagging effect is necessarily slow to respond to changes of magn'etomotive force. If, therefore, the field variations produced by armature reaction are opposed by currents set upinashort-circuited windingor windings in inductive relation to the field, the result is a reaction lagging behind the effect which produced it and greater in magnitude than otherwise would be the case without the use of the short-circuited winding. Suppose this reaction to be set up as the result of an oscillation of the converter-armature. As the armature shifts in one direction the field strengthens, and the armature is driven back and toward the neutral position, passing by the same in the manner already described and moving away from the neutral in the opposite direction, thereby producing an opposite reaction upon the field, which in its turn causes the armature to move back again toward the neutral. Owing, however, to the sluggishness or lag in variations of the field, the movement of the armature away from the neutral does not begin to meet instantly'with opposition, so that on the return oscillation the lagging reaction of the induced currents set up in the short circuits on the field during the forward movement of the armature is added to the pull on the armature, normally acting to drag it back to its neutral position. The retarding effect on the armature while moving away from its neutral position is thus less than the accelerating effect when returning to the neutral position, so that the result is equivalent to the addition of a fresh impulse during each acceleration. In a general way we believe these to be the reasons why a positive disadvantage results from attempting to suppress variations in the value of the field-flux in order to prevent hunting; but we do not hold ourselves responsible for the accuracy of these theoretical deductions and advance the same simply by way of explanation of the facts which we have found to be truein practice. Instead, therefore, of opposing the variations in the field of the converter, as described, we have found it of great advantage over this mode of procedure to oppose only that component which tends to strengthen and weaken the pole-corners without necessarily varying the strength of the fieldin other words, to oppose the crossmagnetizing tendency of the armature reaction. The flux which causes this cross-magnetizing tendency is produced by a magnetomotive force acting between the poles of the converter, and for this reason we have, as above stated, called the fiux thus produced or which the magnetomotive force tends to produce the interpolar flux. By opposing the variation in this flux the variations or causes which produce it are consequently opposed, and the tendency of the converter to hunt is thus greatly reduced and generally entirely eliminated.

We are aware that it has heretofore been proposed to place short circuits both about the field-poles and between the poles in order to intercept both components of the armature reaction. Our invention is a distinct improvement over this construction and involves more than a mere omission of one of the sets of short circuits, since by such omission we secure an improved and more effective means for preventing the above-described hunting of synchronous machines.

From what has been said it will be seen that our invention involves the use of short circuits of suitable form placed between the field poles or tips and omitted from the field proper. These short circuits in the forms employed by us we designate as bridges. Their structure will be best understood by reference to the following description, taken in connection with the accompanying drawings, while the scope of our invention, which involves the use of short circuits of this or other suitable form, will be particularly pointed out in the appended claims.

Figure 1 illustrates the application of bridges to a rotary converter. Fig. 2 is an enlarged view of a bridge. Figs. 3 and 4 illustrate another form of bridge.

In Fig. 1 the pole-tips of the converter are shown as being chamfered at 1-that is to say, they are slightly cut away at their edges opposite the armature of the converter. This allows the bridge 2 to undercut, as it were, the corner of each pole-tip. This construction is best shown in detail in Fig. 2, in which it will appear from inspection that the bridge 2 may thus be fashioned so as to be brought into very close proximity to the armature, and thus intercept the greatest possible number of lines of force emanating from the same and passing into the pole-corners. By causing the sides of the bridge to undercut the pole-corners the flux which passes through the bridge isintensified by reason of the better magnetic circuit formed by the pole-tips, in front of which the edges of the bridge are placed.

Aconvenientmeans for securing the bridges in place consists of hooked projections 3, cast integral with the bridge and in such a position as to embrace the opposing pole-tips, as is clearly shown in Fig. 2. Set-screws at, provided with suitable check-nuts 5, may be used for clamping the bridges in position.

To provide for ventilation,the bridge may be pierced with holes, (indicated at 6 in dotted lines,) or, if desired, the whole central portion of the bridge may be cut away. This latter construction, however, is not quite so desirable as the former, since it reduces the crosssection of available conducting material in the bridge. It is, however, quite eifective.

Fig. 4 shows a form of bridge which for convenience is made from sheet-copper. This bridge consists of a sheet 7 with bent-up ends (indicated at S) and provided with a U -shaped strengtheningrib 9. (Shown in section in dotted lines in Fig. 3.) As in the first form of bridge shown, suitable ventilating-holes 10 are provided in order to permit a circulation of air over the armature, and thus allow the same to cool. This bridge is secured to the pole-pieces, as shown in Fig. 3, and is arranged to be let into the pole-tips, so that the surface near the armature is flush with the polar surfaces. The bridge is fastened in position by means of screws 11, passing through the turned-up ends 8 of the bridge into the lagging currents, the variation of that component only of the armature reaction which exists as'cross-magnetization.

2. The method of preventing hunting of rotary converters which consists in opposing, by substantially non -lagging currents, that component only of the resultant armature reaction which is in phase with the direct-current armature reaction.

3. The method of preventing hunting of a1- ternating-curreut dynamo-electric machines, which consists in permitting the field strength to vary unrestrainedly in response to variation of armature reaction, and opposing variations of armature reaction which do not affect the field strength, by currents set up in circuits of high conductivity and low se1finduction.

at. The method of maintaining synchronous rotation of alternating-current, dynamo-electric machines which consists in opposing a change .in armature reaction of at least one of the machines by current set up in a circuit inductively acted upon by the armature-currents, at the same time permitting the field strength to vary without restraint.

5. The method of preventing variations in speed of an alternating-current dynamo-electric machine,which in normal operation tends to run synchronously with another alternating-current dynamo-electric machine, which consists in opposing the variations in crossmagnetizing armature reaction of such machine by induced currents set up in a circuit or circuits of high electrical conductivity and of quick responsiveness, and allowing the tendency to variation in field strength to remain unopposed.

In witness whereof we have hereunto set our hands this 25th day of August, 1899.

EDWIN W. RICE, JR. ERNST J. BERG. WVitnesses:

BENJAMIN B. HULL, MABEL E. JAooBsoN. 

